Continuous manufacture of nitrobenzene



Dec. 11, 1956 L. o. DUBOIS ETAL CONTINUOUS MANUFACTURE OF NITROBENZENEFiled Dec. 11, 1953 MQQMOFW WENMEOMC 2 manna u zzu m mo.. m....2 v

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064 aux-E IN VENTORS:

LAURENT O.DUBO/S ROBERT N. GA RTSIDE WINFORD B. JOHNSON and.

EDGAR W. SCHNEIDER' ATTORNEY United States Patent CONTINUOUS MANUFACTUREOF NITROBENZENE Laurent 0. Dubois and Robert N. Gartside, Woodbury,Winford B. Johnson, Wenonah, and Edgar W. Schneider, Woodbury, N. J.,assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., acorporation of Delaware 7 Application December 11, 1953, Serial No.397,528

5 Claims. (Cl. 260-645) The present invention relates to the manufactureof nitrobenzene. More particularly, this invention relates to themanufacture of nitrobenzene by a continuous process.

Nitrobenzene is manufactured for a number of uses, the primary use beingas the intermediate in the preparation of aniline. produced byintroducing a charge of benzene into a nitrator, then slowly feeding ina mixed nitrating acid (nitric acid and sulfuric acid), and thereafterdigestingthe reaction mixture in the same vessel. Since the addition ofthe mixed acids requires several hours in order v to avoiduncontrollable rises in temperature, and the digestion period requiresseveral more hours, the apparatus used, particularly the nitrator, hasto be large in order to provide a high production rate, and constantoperator surveillance must be maintained. In addition, an explosionhazard is present at the start of any run due to the large unreactedcharge in the nitrator. In order to insure high conversion, it has beenthe practice to use an excess of the nitrating acid, and the recovery ofthe unreacted nitric acid presented another problem.

It is, accordingly, an object of the present invention to provide aprocess for the preparation of nitrobenzene wherein the foregoingdisadvantages are eliminated. A furtherobject of the present inventionis to provide a process for the preparation of nitrobenzene whereinessentially all of the nitrating acid is consumed. Additional objectswill become apparent as the invention is more fully described.

We have found that the foregoing objects may be achieved by preparingnitrobenzene by a continuous process instead of batchwise, and byproviding for the treatment of the acids separated from the reactionmixture by benzene to strip out essentially all of the nitric. acid, thebenzene thus used being introduced into thenitrator along with thedissolved nitrobenzene formed during the treatment. g

In order to more fully describe our invention, reference is madeto theaccompanying flowsheet which illustrates a simple process for thecontinuous nitration of benzene in accordance with this invention.

In the flowsheet, all of the units are labeled with a descriptive nameand the direction of flow from and to each unit is indicated by an arrowin the connecting lines. For simplicity, obvious details such asregulating valves and pumps have been omitted.

The operation of the process represented by the flowsheet is as follows:Mixed acid is fed from tank 1 to the bottom of the nitrator 4 whilesimultaneously benzene (containing dissolved nitrobenzene after thestart of the process) is fed from charge tank 3, also to the bottom ofnitrator 4. The nitrator 4 is provided with For many years, nitrobenzenehas been 2,773,911 Patented Dec. 11, 1956 ice a conventional agitationmeans to ensure complete mixing of the reactants. The reaction mixtureat the top of nitrator 4, consisting essentially of nitrobenzene,sulfuric acid, water, and some unreacted nitric acid, overflows to thesettling tank 5. Since nitrobenzene is essentially non-miscible with theacid-water solution, and of lower specific gravity, it forms the upperlayer and continuously overflows to the Water wash tank 6 where it isagitated with fresh water. The nitrobenzene-water mixture overflows tosettling tank 7 where separation occurs. Since the specific gravity ofnitrobenzene is greater than that of the wash water, the relatively purenitrobenzene is drawn ofl at the bottom of tank 7 and sent either tostorage or for further processing.

The wash water from settling tank 7 overflows to mixing tank 8, where itis agitated with benzene from charge tank 3. Due to the highersolubility of nitrobenzene in benzene over that in water, substantiallyall of the nitrobenzene will be extracted from the wash water. Themixture from mixing tank 8 overflows to settling tank 9 where the layersseparate, the benzene-nitrobenzene solution forming the top layer andoverflowing to the denitrator 10. The water from settling tank 9 ispurged, preferably to a neutralizing basin.

The residual acids from settling tank 5 .are fed into the denitrator 10also and are there mixed with the benzene solution from settling tank 9.The relatively small quantity of previously unreacted nitric acid isthere consumed to form additional nitrobenzene and the entire mixtureoverflows to the settling tank 11. The sulfuric acid-water solution isdrawn from the bottom of settling tank 11 and transported to a wasteacid recovery area for reconcentration. The upper layer, consisting ofbenzene and dissolved nitrobenzene overflows to the charge tank 3 whereit is mixed with fresh benzene from the storage tank 2 in the amountrequired for the continuous charging of nitrator 4.

In actual construction, settling tanks 5, 7, 9, and ,11, mixing tanks 6and 8, and denitrator 10, may all be combined into a single unit withpartitions forming the required separations, or they may be combinedinto two :or three units having the required partitions. Sucharrangement obviously reduces both the space required and the pipingneeded. The actual apparatus-design is not a part of the presentinvention, which is,-therefore, not limited to any particulararrangement of units.

The greatest amount of reactant recovery occurs at the denitrator 10,and, under some circumstances, it may be unnecessary to include thebenzene treatment of the nitrobenzene wash water. Under such operation,tanks 8 and 9 would be omitted, and the benzene from charge tank 3 orstorage tank 2 would be fed directly to the denitrator 10. Similarly, itwould be completely feasible to feed the benzene solution from settlingtank 9 directly to the charge tank 3 and introduce fresh benzene at thedenitrator 10, the remainder of the process being as previouslydescribed. Another alternative is to introduce the fresh benzene fromstorage tank 2 at mixing tank 8 and use the solution from this tank forthe remaining recovery steps.

The following table illustrates the operation of the nitration stage ofthe present process using fresh benzene. The purpose of these examplesis to demonstrate the range of operating conditions for the nitration ofbenzene in a continuous process, and the constitution of the reactionmixture leaving the nitrator.

Table 1 NB 19. et W t i l Nitrating Reten- Nitra- Nitric y as eacd ayeracid, tion tion acid- Yield, percent time, temp., benzene UnnipercentN01 mm. F. ratio Percent Percent trated Percent Percent Percent PercentPercent Percent NB 1 DNB 3 material, HNO: HsSOt HNO: H3804 NB 1 DNB 1percen 11.00 115 0.945 94.0' 0.06 1.95 3.33 1.56 73.76 1.03 99.0 12.08170 0. 937 97.3 0.20 0.70 1.69 1.24 73.30 0.69 91.5 14.76 116. 0.63388.0 0.11 10.90 0.35 0.89 72.93 0.73 35.4 10. 90 140 0. 917 95. 1 0. 240. 37 4. 27 2. 70 72. 0.65 99. 1 11. 32 140 0. 797 96. 8 0. 0. 42 2.33 1. 73 72. 00 0. 53 95.9 31. 44 140 0. s39 93. 3 0. 22 0. 23 1. 41 0.95 72. 5 0. 51 92. 3 39. 95 140 0. s74 92. s 0. 44 0. 17 2. 4s 1. 37 71.7 0. 26 92. 3 9. 42 140 0, 911 93. s 0. 0. 13 5.88 3. 69. 02 1. 64 97.211.16 130 1.05 89.8 0. 38 0.20 7.35 3.64 71.57 1.75 "99.6 12. 200 0. 75793. 6 0. 39 5. 59 0. 51 0. 15 72.20 1-. 39 100. 0 17. 31 130 1. 17 87. 50. 39 0. 21 11.90 5. 04 71. 11 0. 35 -96. 1 32.43 140 0. s33 95. 2 0.25 1. 96 2. 52 1. 70. 2s 0. 89 100.0 3. 00 135 0.838 95. 6 0. 40 1. 462. 55 2. 00 72. 50 0. 49 97. 2 5. 88 129 0. 864 91.8 0. 14 4. 24 3. 393.33 71. 94 1. 21 95. 7 5. 92 15s 0. 838 95. 5 0. 19 1. 92 2. 47 2. 4271. 99 0. 42 9s. 0 5.95 160 0. 881 95.0 0.21 2.09 2.56 0.72 72.91 0. 4196.0 10. 140 0. 990 90. 2 0. 26 0. 15 9. 05 5. 86 68. 75 0. s5 99. 5

1 Nitrobenzene. Dinitrobenzene.

The foregoing data illustrate efiective nitration of benture from thetop of said reaction zone and transferring zene w1th mixed acld wherein:05 said reaction mixture to a settling zone; (3) continuously (l) Themixed ac1d contalns from approximately 25 removing nitrobenzene from thetop of said settling zone to 50% by weight of n1tr1c acld; and wastemixed acid from the bottom thereof, said (2 The nitric acid to benzenerat1o varies from apwaste mixed acid being transferred to a denitratingzone; proximately 0.6 to 1.2 to 1; (4) continuously introducing benzeneto said denitratin'g (13) The nitration temperature is 1n the range offrom zone and agitating with said waste mixed acid; (5) con- F. to 200tinuously transferring mixture from said denitration zone (4) Theretention time is varied from 3 minutes to toa settling zone; and (6)continuously withdrawing 40 mmutes. from the top of said settling zone asolution of nitro- The following experiment illustrates an analysls ofbenzene in benzene, said solution thereafter being inthe flow dunngseveral phases of the present process. troduoed into said reaction zone.Nitration temperamm o F" 149 2. A process as claimed in claim 1, whereinthe mix- Percent HNO3 in mixed acid 40 ture of nitric acid and sulfuricacid contains from 25 1 to 50% b weight of nitric acid and from 45 to62% Ratio HNOa to benzene 0-83 Percent HNOa in nitrobenzene to tank 64.60 by welght of sulfunc.acld'. I Percent HNOz'in waste acid todenitrator 10 2.56 40 as .wherem 9 ram Percent nitrobenzene in wasteacid to denitrator 10 0.81 0f mmc acid to bFnZene m the reactlon zone 18from Percent HNOs in nitrobenzene to storage 0.003 to by 1 Percentnitrobenzene in benzene from tank 9 6.9 A clfumed m clalm wherem the re-Percent nitrobenzene in Waste acid from action zone is maintained at atemperature between 115 nitrator 10 nil 15 and Percent HNO3 in wasteacid from denitrator 10 0.19 Pmcess'as cla1 med clalm the 1 Percentnitrobenzene in purge from tank 9 020 benzene after separanon from thewaste mixed ac1d 1s Percent nitmbe'nzene in benzene from denitmtorwashed with water, the wash water separated from the 10 1236 washednitrobenzene and agitated with benzene,the mix- 1 Some nitrobenzenecontent due to circulation from charge ture of Wash water and benzenecontaining dissolved nitrobenzene transferred to a settling zone, andthe benzene containing dissolved nitro'oenzene withdrawn and added tothe benzene solution being introduced into said reaction zone.

References-Cited in the file of this patent UNITED STATES PATENTS1,309,577 Holmes July 8, 1919 2,254,352 Cloud et al. Sept. 2, 19412,370,558 Mares Feb. 27, 1945 2,402,180 Papazoni June 18, 1946 2,455,322Teeters et al. Nov. 30, 1948 I it

1. A PROCESS FOR THE MANUFACTURE OF NITROBENZENE WHICH COMPRISES (1)CONTINUOUSLY INTRODUCING SEPARATELY INTO THE BOTTOM OF A REACTION ZONE ASOLUTION OF NITROBENZENE IN BENZENE AND A MIXTURE OF NITRIC ACID ANDSULFURIC ACID; (2) CONTINUOUSLY REMOVING REACTION MIXTURE FROM THE TOPOF SAID REACTION ZONE AND TRANSFERRING SAID REACTION MIXTURE TO ASETTLING ZONE; (3) CONTINUOUSLY REMOVING NITROBENZENE FROM THE TOP OFSAID SETTLING ZONE AND WASTE MIXED ACID FROM THE BOTTOM THEREOF, SAIDWASTE MIXED ACID BEING TRANSFERRED TO A DENITRATING ZONE; (4)CONTINUOUSLY INTRODUCING BENZENE TO SAID DENITRATING ZONE AND AGITATINGWITH SAID WASTE MIXED ACID; (5) CONTINUOUSLY TRANSFERRING MIXTURE FROMSAID DENITRATION ZONE TO A SETTLING ZONE; AND (6) CONTINUOUSLYWITHDRAWING FROM THE TOP OF SAID SETTLING ZONE A SOLUTION OFNITROBENZENE IN BENZENE, SAID SOLUTION THEREATER BEING INTRODUCED INTOSAID REACTION ZONE.